Cold spraying is a relatively new low temperature coating technology that holds promise for use in repair applications of aerospace components. Cold spraying is a coating process which uses a high pressure (4 to 5 MPa) and preheated (up to 1000° C.) gas stream (for example, nitrogen or helium) to accelerate micro-particles (15 to 60 μm diameter) via a converging-diverging nozzle (de Laval) to supersonic speeds (approximately 600 to 1000 m/s) and then to impact the particles onto the substrate. The micro-particles will then plastically deform, undergo rapid interfacial melting and bond with the substrate, forming the coating.
However, a conventional cold spray nozzle arrangement, as shown in FIG. 1, only allows coating particles 10 to have perpendicular impact with the substrate 130. This results in a base section of the coating particles 10, indicated at ‘A’ in FIG. 1, having a strong bond with the substrate, but leaving the side portions, indicated at ‘B’ in FIG. 1, of the coating particles 10 either unbonded or only weakly bonded to the substrate 130. This is also confirmed by fractographic images where the side portions of the particles 10 show little bonding to the substrate 130.